RNA hairpins in noncoding regions of human brain and Caenorhabditis elegans mRNA are edited by adenosine deaminases that act on RNA

Adenosine deaminases that act on RNA (ADARs) constitute a family of RNA-editing enzymes that convert adenosine to inosine within double-stranded regions of RNA. We previously developed a method to identify inosine-containing RNAs and used it to identify five ADAR substrates in Calenorhabditis elegans. Here we use the same method to identify five additional C elegans substrates, including three mRNAs that encode proteins known to affect neuronal functions. All 10 of the C elegans substrates are edited in long stem-loop structures located in noncoding regions, and thus contrast with previously identified substrates of other organisms, in which ADARs target codons. To determine whether editing in noncoding regions was a conserved ADAR function, we applied our method to poly(A)(+) RNA of human brain and identified 19 previously unknown ADAIR substrates. The substrates were strikingly similar to those observed in C elegans, since editing was confined to 3' untranslated regions, introns, and a noncoding RNA. Also similar to what was found in C elegans, 15 of the 19 substrates were edited in repetitive elements. The identities of the newly identified ADAR substrates suggest that RNA editing may influence many biologically important processes, and that for many metazoa, A-to-I conversion in coding regions may be the exception rather than the rule.